Field of the Invention
Embodiments of the invention pertain to the field of microelectromechanical systems (MEMS) and more particularly to magnetic field sensing using MEMS.
Description of the Related Art
Magnetic sensors can be found in many applications across a wide range of industries. For example, magnetic sensors can be found in automotive, consumer, industrial, medical, and aerospace applications. The magnetic sensor may be used to determine the orientation of a device with respect to its environment. In consumer applications, they can be found as sensors to detect when devices (e.g., cell phones, laptop computers, doors, etc.) are opened or closed. In addition, cell phones incorporate magnetic sensors to provide an electronic compass and navigation capability to complement GPS tracking. A relatively wide bandwidth magnetic sensor can be combined with an accelerometer to make a gyroscope.
Many different approaches have been used to detect magnetic fields including giant magneto-resistance (GMR), Fluxgate, anisotropic magnetoresistance (AMR), and Hall effect sensors, which exploit the Hall effect. Of those approaches, only Hall, GMR, and AMR sensors are capable of integration with integrated circuits, which provides a small form factor. In Hall effect sensors, when a voltage is applied across a semiconductor material, charge carriers begin to flow. If a magnetic field is applied orthogonal to the surface of the semiconductor material, the current carriers deflect to the side because of the Lorentz force causing a charge to build up on one side of the material. That results in a voltage across the semiconductor material orthogonal to the current carrier flow. The resulting Hall voltage is a measure of the magnetic field. A Hall effect sensor system may include a magnetic concentrator, e.g., a ferromagnetic material that is deposited on a surface of a semiconductor wafer over the Hall effect sensor to enhance the magnetic field. While Hall effect sensors are widely used, they can be bulky, particularly if magnetic field sensing in three axes is desirable. The Hall sensor system may occupy considerable space and depending on the application, can often require a separate integrated circuit.
Accordingly, improved magnetic sensors that are small and efficient are desirable.